Generally speaking, as the DC voltages needed by the motherboard and the peripheral devices (such as the floppy disc drive, hard disc drive, optical disc drive, electric fan, etc.) of the computer are variant, the power supply, which provides the DC power for the computer system, has to output at least two different levels of DC power to satisfy the variant voltage demands of various devices in the computer system.
Recently, as the computer's working speed demanded by the user becomes higher and higher, the electric power needed by CPU and the peripheral devices in the computer system grows responsively; therefore, the power supply of the computer system has to provide more power output. Among various computer designs, the power of the output ports may have an energy-limiting level (maximum output power Max VA) in some systems; thus, these output ports need the design of multiple sets of current-limiting compare units to satisfy those users who demand high-grade safety standard. As the computer systems shift rapidly and the power demand of many peripheral devices is higher and higher, the high-grade safety standard mentioned above may not be satisfied. If a power supply has the aforementioned design, the peripheral devices that can be installed to the computer will be limited. Therefore, the power supply needed by the user is one having selectable single set or multiple sets of current-limiting compare functions for the output ports. As shown in FIG. 1, in this prior art, each of select circuits having switch function is electrically coupled to each current-limiting compare unit, which enables the user to determine whether single set or multiple sets of disable/protect functions for current limiting are to be adopted according to the powers needed by the peripheral devices. Most of the abovementioned problems can be solved by this prior art; however, as it is performed via manual operation, the performance thereof still has room for improvement.